1. Field of the Invention
This invention relates to a process of manufacturing spacer frames for perimeter-bonded insulating glass panes wherein tubular metal bars filled with a desiccant are bent around an axis which is at right angles to two parallel cheeks of the tubular bar.
2. Description of the Prior Art
A perimeter-bonded insulating glass pane comprises two individual glass panes, which are spaced apart and bonded to an interposed spacer frame. The spacer frames usually consist of tubular metal bars, made in most cases of special steel or aluminum and filled with a desiccant in order to keep the residual moisture trapped in the insulating glass pane so low that a temperature drop will not result in a condensation of water on the inside surfaces of the insulating glass pane. When the spacer frames have been assembled and filled with the desiccant, they are coated on both cheeks with a long-lasting adhesive and sealing compound, which in most cases consists of polyisobutylene and which when the spacer frame has been placed between two individual glass panes will adhere to the latter so that the components of the insulating glass pane will be firmly held together.
The hollow spacer frame is filled in most cases with a granular desiccant which trickles easily. The desiccant usually consists of molecular sieve but may also consist of silica gel.
Most the spacer frames are made from straight tubular bars, which are first filled with the desiccant and are closed at their ends with a plug, e.g., of foamed rubber, and are then assembled to form a closed frame in that corner-forming angles are inserted into the ends of the bars. But the use of corner-forming angles involves several disadvantages: The assembling of the spacer frames must be performed in numerous steps. The joints of the corner-forming angles are often rather unstable and require a particularly careful application of the adhesive and sealing agent to the side faces of the spacer frame.
In the present description and the claims, the term cheeks is used to describe those parallel wall portions of the tubular bars or of the spacer frames comprising said bars which in the complete insulating glass pane are joined by an adhesive to the two individual glass panes.
It has also been proposed to manufacture the spacer frames from a single tubular bar, which is bent to form the corner portions so that each spacer frame has only a single joint, which can be closed by a connector. That joint may be disposed at a corner of the frame or between two adjacent corners.
It is not easy to bend tubular bars to a small-radius bend and such bending is even more difficult in the present case because the tubular bars are filled with a granular desiccant, which is almost incompressible. Whereas it has already been proposed to fill the spacer frames with the desiccant after the corner portions have been formed, that procedure is rather expensive because each of the four bars of the spacer frame must be opened, filled and then re-sealed.
When tubular bars filled with desiccant are to be bent, the problem will arise that the desiccant in the corner portions will be subjected to a progressively increasing pressure as the bending proceeds. Because the desiccant is incompressible, that application of pressure often causes the tubular bar to burst. In order to avoid such bursting, it has already been proposed (in German Patent Publication No. DE-28 29 444 A1) to bend the corner portions to the shape of a quadrant of a circle having a relatively large radius. Whereas that practice will preclude a bursting of the tubular bar in the corner portions of the spacer frame, it involves other disadvantages: The edge gap formed in the corner portions of the insulating glass panes will be much deeper than the edge gap at the straight portions of the spacer frame, and it is very difficult to fill said deep edge gaps with one of the sealing agents which are usually employed to seal perimeter-bonded insulating glass panes and have the consistency of a high-viscosity paste. Besides, the quadrant-shaped corner portions of the frame will be conspicuous if the insulating glass pane is installed into a rectangular sash having no rounded corners unless the rabbet of the sash is so deep that it covers also the quadrant-shaped corner portions of the spacer frame.
It has also been proposed to form the tubular bars in the inner walls of the corner-forming portions with slots by means of a milling cutter when the tubular bars have been filled with the desiccant and before they are bent. The position of the slot exactly defines the apex of the corner portion and slightly facilitates the bending operation but it does not prevent the bursting of the tubular bar on the outside if the radius of bend is small.
It has also been proposed to cut open the desiccant-filled tubular bar at the location of the apex of a subsequently formed corner portion and to remove a small quantity of desiccant from the tubular bar by an air blast directed to the opening. This procedure will reduce the risk of a bursting of the tubular bars during the bending operation.
But the two methods described last hereinbefore have the disadvantage that the configuration, width and location of the slots must be carefully selected in order to ensure that they will be automatically closed during the bending operation so that desiccant can no longer escape after the bending operation. That requirement cannot always be met. Besides, the slots formed in the corner portions of the spacer frames reduce the strength of the spacer frames, which inherently do not have a very high strength.